1. Field of the Invention
The invention relates to a multicolor or full color image formation apparatus, such as a printer, a copying machine, and a facsimile, and an image formation method.
2. Description of the Prior Arts
A conventional four drum type configuration, which comprises four light sensitive elements provided with one each developing device, used in a full color image formation apparatus utilizing an electrophotography method is disclosed in Japanese Unexamined Patent Publication JP-A 58-95361(1983).
The image formation apparatus disclosed in the official gazette comprises a first process portion for forming an image with a first color 101, a second process portion for forming an image with a second color 102, a third process portion for forming an image with a third color 103, and a fourth process portion for forming an image with a fourth color 104 as illustrated in FIG. 10.
The first process portion 101 comprises a light sensitive element 105, a charger 106 for charging the light sensitive element 105, and a developing device 107 for developing on the basis of an electrostatic latent image formed on the light sensitive element 105. Accordingly, when a laser beam 108 modulated by an image signal is irradiated to a rotating polygon (rotating polygon mirror), which is not illustrated, the laser beam 108 reflected by the polygon is irradiated to the light sensitive element 105 via a reflection mirror, which is not illustrated.
At the time, the light sensitive element 105 is exposed and scanned by the laser beam 108 with respect to the axis direction of the light sensitive element 105. As a consequence, an electrostatic latent image is formed on the light sensitive element 105, and is developed with a developing device 107 on the basis of the electrostatic latent image. Then the image developed by the developing device 107 is transferred on a paper (not illustrated) conveyed by a paper conveyor belt 110 with a transfer unit 109. The light sensitive element 105 after transfer is cleaned by a cleaning blade 111, and the charge thereof is eliminated with a charge eliminator (not illustrated) as needed. Then the light sensitive element 105 is again charged by a charger 106. Since the configuration and operation of the second process portion 102, the third process portion 103, and the fourth process portion are the same as those of the first process portion 101, explanation thereof is not provided herein.
Accordingly, in the image formation apparatus, color images formed by the first to fourth process portions 101, 102, 103 and 104 are transferred successively on a paper to conduct a multicolor copy. In the image formation apparatus, two laser beams are irradiated to a polygon so as to expose and scan two light sensitive elements to the opposite directions by the rotation of the polygon. Accordingly, four light sensitive elements can be exposed with two polygons, and in the official gazette, the device is downsized by providing a minimum number of polygons.
Furthermore, as a full color image formation apparatus, one comprising four developing devices arranged in the vicinity of one light sensitive element is known (not illustrated). As these kind of devices, one utilizing a light sensitive element exposing device and one utilizing two light sensitive element exposing devices are included.
In an image formation apparatus utilizing a light sensitive element exposing device, a full color image is obtained by transferring an image in one color developed with one developing device to a transfer paper or a transfer medium by rotating a light sensitive element, and conducting the same process for the other colors. Accordingly, since a full color image is obtained by rotating the light sensitive element for four times in the device, it is called a four rotation process type image formation apparatus.
An image formation apparatus, which comprises two light sensitive element exposing devices, provided with four each developing devices is disclosed in Japanese Unexamined Patent Publication JP-A 6-143701(1994). Since the device comprises two light sensitive element exposing devices, a two color image can be formed at the same time with respect to one light sensitive element, and thus a full color image can be obtained by rotating the light sensitive element twice.
Furthermore, examples of two color electrophotography copying devices are disclosed in Japanese Unexamined Patent Publications JP-A 59-123861(1984) and JP-A60-59373(1985).
In a device disclosed in the former official gazette, a first color image and a second color image are formed on two light sensitive elements, respectively. A copying paper is conveyed by a copying paper conveyor belt provided so as to contact with the two light sensitive elements. The images are transferred on the conveyed copying paper. The device is designed so that the diameter of one light sensitive element is smaller than the diameter of the other light sensitive element for downsizing and cost reduction of the device.
In a device disclosed in the latter official gazette, as in the above reference, two light sensitive elements having different diameter sizes are provided. A first developing device for developing a first color is provided adjacent to one light sensitive element, and a second developing device for developing a second color and a third developing device for developing a third color are provided adjacent to the other light sensitive element. In this device, while the second color developing device is in operation, the third developing device does not function, and while the third color developing device is in operation, the second developing device does not function.
According to the configuration, by the use of two light sensitive elements having different diameter sizes, downsizing and cost reduction of the device is achieved as in the above reference. Moreover, since a second color and a third color can be optionally changed, color image of various modes can be provided.
However, in the configuration of the four drum type image formation apparatus disclosed in Japanese Unexamined Patent Publication JP-A 58-95361(1983), since four light sensitive elements are provided each with a charger, a developing device and a transfer unit, the number of parts is large. Thus, the device is enlarged so that a problem of cost increase of the device is generated.
Further, in the configuration of a four rotation process type image formation apparatus using one light sensitive element exposing device or the configuration of an image formation apparatus in Japanese Unexamined Patent publication JP-A 6-143701(1994), since four developing devices are arranged in the vicinity of one light sensitive element, a large light sensitive element is necessary. As a consequence, a problem occurs in that the device itself needs to be large.
In particular, in the former of the image formation apparatuses, since one image is formed by one rotation of a light sensitive element, in order to obtain a full color image, the light sensitive element needs to the rotated four times for forming four images successively one by one. Accordingly, there is a problem in that a long time is required for obtaining a full color image.
In the configurations disclosed in Japanese Unexamined Patent Publications JP-A 59-123861(1984) and JP-A 60-59373(1985), although downsizing and cost reduction of the devices are achieved, the apparatus disclosed in the both official gazettes are a two color electrophotographic copying device. Thus, downsizing or cost reduction of a full color image formation apparatus is not achieved.
Image formation apparatus where a full color image is formed by scanning an original with two optical systems are disclosed in Japanese Unexamined Patent Publication JP-A 60-169862(1985) and Japanese Examined Patent Publication JP-B28-33685(1996). Since image formation apparatus shown in the gazettes comprise two optical systems for scanning an original, the configuration of the device is complicated and a problem is generated in that the device itself needs to be large. Besides, in the configuration of an image formation apparatus disclosed in the latter of the official gazettes, since three developing devices are provided in the vicinity of one light sensitive element in two sets, the image formation portion becomes large and a problem is generated in that the device needs to be large.